1. Field of the Invention
The invention relates generally to directional drilling tools. In particular, the invention relates to directional drilling tool that are used to control the direction of drilling of bore holes.
2. Background Art
Increasingly, the drilling of oil and gas wells is no longer a matter of drilling vertically straight boreholes. Changes in the direction of drilling of boreholes are required for a number of reasons. The most frequent reason is to change from vertical drilling to horizontal drilling or drilling at any angle therebetween. Horizontal drilling has been known for many years and there are a number of established methods of changing the direction from vertical drilling to horizontal drilling. Technology and techniques have now been developed to change the angle of the bore's trajectory by up to and sometimes exceeding 90 degrees from the vertical. Directional drilling using coiled tubing rather than jointed pipe can offer numerous advantages compared to conventional drilling including new approaches to oil and gas traps having non-conventional geometries, economic zone enhancement as can occur, for example, if the borehole is deviated to actually follow an oil or gas bearing strata, improved economics particularly in an under-balanced environment (when formation pressure is sufficient to force hydrocarbons to the surface at potentially explosive rates) and reduced environmental degradation.
The most common existing method to change the direction of drilling is to use a bent support (often called a “bent sub”) for the drill bit. Typically a drill bit powered by a motor is used with a bent sub positioned behind the motor. It is also possible for the bent sub to be positioned in front of the motor. The bent sub effectively causes the axis of rotation of the drill be to be at a different angle to that of the drill pipe. Continuous drilling with the bent sub causes continuous changes of direction which results in a curved well hole in the direction of the bend of the bent sub. When the required curvature has been achieved drilling can be stopped and the bent sub changed for a straight sub to resume straight drilling. Alternatively, the entire drill pipe can be rotated at the surface resulting in a small rotation of the bent sub, motor and drill bit assembly. In that case, the bend of the bent sub will be positioned in a different direction and drilling can be resumed in a different direction. Positional sensors such as gyroscopic sensors are often used to check the progress and direction of the drilling to establish what adjustments to the drilling angle are required.
After deviating a borehole from the vertical, it is not typically practical to sustain continuous drilling operations by rotating the drill string in order to also rotate the bit. Preferably only the bit is rotated by a downhole motor attached to the lower end of the drill pipe. The motor typically includes a rotor-stator that generates torque as drilling fluid passes between the rotor and stator. A bent sub may be positioned behind or in front of the motor. As discussed above, the bent sub deviates the hole by the required amount and may surround a drive shaft that transmits the rotor/stator's torque to a bearing assembly.
Electronics supported in the bottomhole assembly and connected to the surface by a wire line passing through the interior of the drill string can transmit information with respect to the amount of curvature in the borehole's trajectory so that it may be plotted. Once the required curvature has been attained so that the axis of the bit's rotation is pointed in the desired direction, the drilling is stopped and the motor is withdrawn from the well. The bent housing is then either removed or straightened (if it is of the adjustable sort) and the motor is tripped back into the hole to resume drilling. Each time the motor requires service, or a change in the hole's direction is required, this process must be repeated. This results in substantial costs and down time largely due to the time required to make and break all of the joints as the drill string is tripped in and out of the hole. For this reason, jointed drill pipe is now being replaced whenever possible with coiled tubing.
To drill a short radius or medium radius wellbore it is desirable to be able to drill with relative precision along desired or predetermined wellbore paths (“wellbore profiles”), and to alter the drilling direction downhole without the need to retrieve the drilling assembly to the surface. Sufficient torque is needed to rotate the bent sub, drill bit, and any downhole tools disposed below the orienting tool. Drilling assemblies for use with coiled tubing to drill wellbores in the manner described above, preferably need a dedicated orienting device. The orienting device may be located near the drill bit for orienting and controlling the drill bit while drilling the wellbore. The device should be operable during drilling of the wellbore to cause the drill bit to alter the drilling direction.
In addition to controlling the bend angle in the coil tubing, it is also necessary to orient the bend point to control and adjust the borehole's bearing or azimuth. Examples of orienting tools for controlling azimuth are disclosed in U.S. Pat. Nos. 6,955,231, 5,894,896, and 5,441,119.
U.S. Pat. No. 6,955,231 describes a tool for changing the direction of drilling during drilling positioned between drill string and a bent sub. The tool includes at least two housing elements connected to one another, a passage for drilling fluid, a valve adapted for choking the passage so that the tool can be activated for rotation, and a piston adapted for forced guiding of the rotation. Twisted splines may be formed in the wall of the passage and in the wall of the opposite piston to guide rotation of the piston. The tool is activated for rotation by increasing the pressure of the fluid passing through the tool. The rotation ends by relief of the pressure of the fluid. The tool rotation is infinitely variable and is only regulated by monitoring magnetic measurements recorded by measurements-while-drilling (MWD) instruments and techniques.
U.S. Pat. No. 5,894,896 describes an apparatus for azimuthal orientation of a tool in a wellbore. The apparatus includes a tubular housing, a mandrel rotatably supported in the tubular housing and extending therefrom for connection to a toll for rotation, a piston mandrel axially aligned with and connected to the mandrel, and a piston longitudinally movable in an annulus between the piston mandrel and the tubular housing that is non-rotatable relative to the tubular housing. At least one pin is longitudinally movable in concert with the piston arranged to track in respective helical grooves in the mandrel. A flow path selectively delivers pressurized hydraulic fluid to either side of the piston for rotating the mandrel or to both sides of the piston equally to maintain a fixed annular orientation. The orienting tool is independently controlled from the mud flow rate.
U.S. Pat. No. 5,441,119 describes a directional drilling system including a directional drilling tool that has two parts moveable relative to each other in the horizontal or vertical planes. Cam surfaces are provided between the two parts for adjustments to the drilling direction in the vertical plane. A slot and groove mechanism is provided between the two as an example of adjustments in the horizontal plane. The cam surfaces are contoured such that, when the piston and inner parts are rotated with respect to each other, an inner part is adjusted to a position which is off line with respect to the original center line and the center of the drill pipe. Thus, the entire orienting device rotates and moves off center of the drill pipe.
Accordingly, there exists a need for an orienting apparatus that provides sufficient torque output to downhole tools disposed below (further downhole) the orienting apparatus. There also exists a need for an orienting apparatus that allows controlled, accurate rotation of the apparatus, and therefore downhole tools located below the orienting apparatus, from the surface.